*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}
li {
    list-style: none;
}
.app {
    width: 400px;
    margin: 150px auto;
}
.app .app-main {
    box-shadow: 0 1px 6px 0 rgba(0, 0, 0, 0.2);
}